No, the Atari ST is not natively 60Hz, at least not in Europe so this would no real impact. Also depending on the type of game the YT cap of 30fps may not affect it, for example if it's a 3d game that runs below 30fps (which most amiga/Atari games do), smooth scrolling platformers and shooters may be different thought. I've kept everything locked to 30fps, it's a real shame youtube doesn't support 50/60 fps..